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Abstract:

An electromechanical systems array includes a substrate and a plurality
of electromechanical systems devices. Each electromechanical systems
device includes a stationary electrode, a movable electrode, and an air
gap defined between the stationary electrode and the movable electrode,
where the air gap defines open and collapsed states. At least two
different electromechanical systems device types correspond to finished
devices having different sized air gaps when in the open state. Each
electromechanical systems device further includes a primary mechanical
layer of a common thickness along with one or more mechanical sub-layers
with a different cumulative thickness for each of the at least two
different electromechanical systems device types. The mechanical
sub-layers can be deposited for use as etch stops during processing of
the air gap. The different air gap sizes of each electromechanical
systems device type can correspond to a different mechanical sub-layer
thickness.

Claims:

1. An electromechanical system comprising: a substrate; and a plurality
of electromechanical devices, each electromechanical device comprising: a
stationary electrode; a movable electrode; and a collapsible gap defined
between the movable electrode and the stationary electrode, the gap
defining at least open and collapsed states; wherein the
electromechanical devices include at least two electromechanical device
types having different gap sizes when in the open state, and the movable
electrode for at least two of the electromechanical device types includes
one or more mechanical sub-layers facing the gap, the cumulative
thickness of the mechanical sub-layers being different for each of the at
least two electromechanical device types.

2. The electromechanical system of claim 1, wherein the one or more
mechanical sub-layers of each of the at least two electromechanical
device types include one or more etch stop layers.

3. The electromechanical system of claim 1, wherein the one or more
mechanical sub-layers of each of the at least two electromechanical
device types include aluminum oxide.

4. The electromechanical system of claim 1, wherein the stationary
electrode of each of the at least two electromechanical device types
includes one or more optical layers facing the gap, the cumulative
thickness of the optical layers being different for each of the at least
two electromechanical device types.

5. The electromechanical system of claim 4, wherein the cumulative
thickness of the one or more mechanical sub-layers and the optical layers
is constant for each of the electromechanical device types.

6. The electromechanical system of claim 5, wherein the one or more
optical layers of each of the at least two electromechanical device types
include the same material as the one or more mechanical sub-layers.

7. The electromechanical system of claim 1, wherein the at least two
electromechanical device types comprise: a first electromechanical device
type having a first gap size when in the open state; and a second
electromechanical device type having a second gap size when in the open
state, the second gap size being larger than the first gap size, wherein
the cumulative thickness of the one or more mechanical sub-layers for the
first electromechanical device type is greater than the cumulative
thickness of the one or more mechanical sub-layers for the second
electromechanical device type.

8. The electromechanical system of claim 7, wherein: the one or more
mechanical sub-layers for the first electromechanical device type and the
movable electrode for the first electromechanical device type form a
mechanical layer for the first electromechanical device type having a
first stiffness; and the one or more mechanical sub-layers for the second
electromechanical device type and the movable electrode for the second
electromechanical device type form a mechanical layer for the second
electromechanical device type having a second stiffness, the first
stiffness being greater than the second stiffness.

9. The electromechanical system of claim 1, further comprising at least
one electromechanical device type without a mechanical sub-layer.

10. The electromechanical system of claim 1, wherein each
electromechanical device includes an interferometric modulator.

11. The electromechanical system of claim 1, wherein the at least two
electromechanical device types includes an interferometric modulator
configured to reflect red light when in the open state, an
interferometric modulator configured to reflect blue light when in the
open state, and an interferometric modulator configured to reflect green
light when in the open state.

12. The electromechanical system of claim 1, further comprising: a
display including one or more electromechanical system; a processor that
is configured to communicate with the display, the processor being
configured to process image data; and a memory device that is configured
to communicate with the processor.

13. The electromechanical system of claim 12, further comprising: a
driver circuit configured to send at least one signal to the display.

14. The electromechanical system of claim 13, further comprising: a
controller configured to send at least a portion of the image data to the
driver circuit.

15. The electromechanical system of claim 12, further comprising: an
image source module configured to send the image data to the processor.

16. The electromechanical system of claim 15, wherein the image source
module includes at least one of a receiver, transceiver, and transmitter.

17. The electromechanical system of claim 12, further comprising: an
input device configured to receive input data and to communicate the
input data to the processor.

18. A method of manufacturing at least a first electromechanical device
and a second electromechanical device, in a first region and a second
region, respectively, the method including: providing a substrate;
forming a stationary electrode layer over the substrate; forming a first
sacrificial layer over the stationary electrode layer in the first
region; forming a first stiffening layer over the first sacrificial layer
in the first region; forming a second sacrificial layer over the
stationary electrode layer in the second region, the second sacrificial
having a different thickness than that of the first sacrificial layer;
and forming a movable electrode layer over the first and second
sacrificial layers, respectively.

19. The method of claim 18, further comprising: forming a second
stiffening layer over the first stiffening layer in the first region and
over the second sacrificial layer in the second region; and forming a
third sacrificial layer over the stationary electrode layer in a third
region, the third sacrificial layer having a different thickness than
that of the first and second sacrificial layers; wherein forming the
movable electrode layer further includes forming the movable electrode
layer over the third sacrificial layer.

20. The method of claim 19, further comprising using each of the first
and second stiffening layers as etch stops in forming at least one
subsequently formed layer.

21. The method of claim 19, wherein forming the movable electrode layer
includes: forming the movable electrode layer on the second stiffening
layer in the first region, wherein the movable electrode layer, the first
stiffening layer, and the second stiffening layer form a first mechanical
layer in the first region; forming the movable electrode layer on the
second stiffening layer in the second region, wherein the movable
electrode layer and the second stiffening layer form a second mechanical
layer in the second region; and forming the movable electrode layer on
the third sacrificial layer in the third region, wherein the movable
electrode layer forms a third mechanical layer in the third region.

22. The method of claim 21, further comprising: forming the first
stiffening layer over the stationary electrode in the second and third
regions; and forming the second stiffening layer over the second
sacrificial layer in the second region, and over the first stiffening
layer in the third region.

23. The method of claim 22, wherein: forming the second sacrificial layer
includes forming the second sacrificial layer over the first stiffening
layer in the second region; and forming the third sacrificial layer
includes forming the third sacrificial layer over the second stiffening
layer in the third region.

24. The method of claim 21, wherein the second sacrificial layer is
thicker than the first sacrificial layer and the third sacrificial layer
is thicker than the second sacrificial layer.

25. The method of claim 24, wherein: the second mechanical layer in the
second region is less stiff than the first mechanical layer in the first
region; and the third mechanical layer in the third region is less stiff
than the second mechanical layer in the second region.

26. The method of claim 19, wherein a third electromechanical device is
formed in the third region, and wherein each of the first, second and
third electromechanical devices include an interferometric modulator.

27. The method of claim 26, wherein the first, second, and third
electromechanical devices include interferometric modulators configured
to reflect green light, red light, and blue light, respectively in an
open state.

28. An electromechanical system comprising at least a first
electromechanical device and a second electromechanical device, the
electromechanical system comprising: means for supporting the first and
second electromechanical devices; means for defining a first gap for the
first electromechanical device; means for defining a second gap for the
second electromechanical device, the second gap having a different size
than the first gap; means for selectively collapsing and opening the
first gap for the first electromechanical device; means for selectively
collapsing and opening the second gap for the second electromechanical
device; first stiffening means for stiffening the means for selectively
collapsing and opening the first gap, the first stiffening means facing
the first gap; and second stiffening means for stiffening the means for
selectively collapsing and opening the second gap, the second stiffening
means facing the second gap and providing a different stiffness from the
first stiffening means.

29. The electromechanical system of claim 28, wherein the each of the
means for selectively collapsing and opening the first and second gaps
includes a first electrode and a second electrode on opposite sides of
the respective gap.

30. The electromechanical system of claim 29, further comprising: first
etch stop means on the first electrode of the means for selectively
collapsing and opening the first gap; and second etch stop means on the
first electrode of the means for selectively collapsing and opening the
second gap, wherein the first electrode of the means for selectively
collapsing and opening the first gap is positioned under the second
electrode of the means for selectively collapsing and opening the first
gap; and wherein the first electrode of the means for selectively
collapsing and opening the second gap is positioned under the second
electrode of the means for selectively collapsing and opening the second
gap.

31. The electromechanical system of claim 28, wherein the second gap is
bigger than the first gap and wherein the second stiffening means
provides a stiffness greater than the first stiffening means.

32. The electromechanical system of claim 31, wherein: the first etch
stop means on the first electrode of the means for selectively collapsing
and opening the first gap includes the same material as the first
stiffening means; and the second etch stop means on the first electrode
of the means for selectively collapsing and opening the second gap
includes the same material as the second stiffening means.

33. The electromechanical system of claim 32, wherein the first etch stop
means has a different thickness than the second etch stop means.

34. The electromechanical system of claim 28, wherein the means for
defining the first gap includes one or more support structures adjacent
the first gap, and wherein the means for defining the second gap includes
one or more support structures adjacent the second gap.

35. The electromechanical system of claim 28, wherein the first
stiffening means includes one or more dielectric layers and wherein the
second stiffening means includes one or more dielectric layers, the
second stiffening means including a different number of dielectric layers
than the first stiffening means.

36. The electromechanical system of claim 35, wherein the one or more
dielectric layers include aluminum oxide.

Description:

CLAIM OF PRIORITY

[0001] This application claims the benefit of U.S. Provisional Patent
Application No. 61/435,701, filed Jan. 24, 2011, which is incorporated in
its entirety by reference herein.

TECHNICAL FIELD

[0002] This disclosure relates to electromechanical systems arrays with
multiple device types of different gap sizes having mechanical layers
that differ in material properties.

DESCRIPTION OF THE RELATED TECHNOLOGY

[0003] Electromechanical systems include devices having electrical and
mechanical elements, actuators, transducers, sensors, optical components
(e.g., mirrors) and electronics. Electromechanical systems can be
manufactured at a variety of scales including, but not limited to,
microscales and nanoscales. For example, microelectromechanical systems
(MEMS) devices can include structures having sizes ranging from about a
micron to hundreds of microns or more. Nanoelectromechanical systems
(NEMS) devices can include structures having sizes smaller than a micron
including, for example, sizes smaller than several hundred nanometers.
Electromechanical elements may be created using deposition, etching,
lithography, and/or other micromachining processes that etch away parts
of substrates and/or deposited material layers, or that add layers to
form electrical and electromechanical devices.

[0004] One type of electromechanical systems device is called an
interferometric modulator (IMOD). As used herein, the term
interferometric modulator or interferometric light modulator refers to a
device that selectively absorbs and/or reflects light using the
principles of optical interference. In some implementations, an
interferometric modulator may include a pair of conductive plates, one or
both of which may be transparent and/or reflective, wholly or in part,
and capable of relative motion upon application of an appropriate
electrical signal. In an implementation, one plate may include a
stationary layer deposited on a substrate and the other plate may include
a metallic membrane separated from the stationary layer by an air gap.
The position of one plate in relation to another can change the optical
interference of light incident on the interferometric modulator.
Interferometric modulator devices have a wide range of applications, and
are anticipated to be used in improving existing products and creating
new products, especially those with display capabilities.

SUMMARY

[0005] The systems, methods and devices of the disclosure each have
several innovative aspects, no single one of which is solely responsible
for the desirable attributes disclosed herein.

[0006] One innovative aspect of the subject matter described in this
disclosure can be implemented in an electromechanical system. The system
includes a substrate and a plurality of electromechanical devices. Each
electromechanical device includes a stationary electrode, a movable
electrode, and a collapsible gap. The collapsible gap is defined between
the movable electrode and the stationary electrode, and the gap defines
at least open and collapsed states. The electromechanical devices further
include at least two electromechanical device types having different gap
sizes when in the open state. The movable electrode for at least two of
the electromechanical device types includes one or more mechanical
sub-layers facing the gap. The cumulative thickness of the mechanical
sub-layer(s) is a different thickness for each of the at least two
electromechanical device types.

[0007] In some implementations, the one or more mechanical sub-layers of
each of the at least two electromechanical device types can include one
or more etch stop layers. Furthermore, the stationary electrode of each
of the at least two electromechanical device types can include one or
more optical layers facing the gap, the cumulative thickness of the
optical layers being different for each of the at least two
electromechanical device types.

[0008] Another innovative aspect can be implemented in a method of
manufacturing at least a first electromechanical device, a second
electromechanical device, and a third electromechanical device in first,
second, and third regions, respectively. The method includes providing a
substrate, forming a stationary electrode layer over the substrate;
forming a first sacrificial layer over the stationary electrode layer in
the first region, forming a first stiffening layer over the first
sacrificial layer in the first region, and forming a second sacrificial
layer over the stationary electrode layer in the second region. The
second sacrificial layer has a different thickness than that of the first
sacrificial layer. The method further includes forming a second
stiffening layer over the first stiffening layer in the first region and
over the second sacrificial layer in the second region. The method
further includes forming a third sacrificial layer over the stationary
electrode layer in the third region. The third sacrificial layer has a
different thickness than that of the first and second sacrificial layers.
The method further includes forming a movable electrode layer over the
first, second and third sacrificial layers, respectively.

[0009] In some implementations, at least one electromechanical device type
can be configured to not have a mechanical sub-layer. Furthermore, the at
least two electromechanical device types can include an interferometric
modulator configured to reflect red light when in the open state, an
interferometric modulator configured to reflect blue light when in the
open state, and an interferometric modulator configured to reflect green
light when in the open state. The method can further include forming a
second stiffening layer over the first stiffening layer in the first
region and over the second sacrificial layer in the second region. The
method can further include forming a third sacrificial layer over the
stationary electrode layer in a third region, the third sacrificial layer
having a different thickness than that of the first and second
sacrificial layers. Furthermore, forming the movable electrode layer
further can include forming the movable electrode layer over the third
sacrificial layer. Forming the movable electrode layer can include
forming the movable electrode layer on the second stiffening layer in the
first region. The movable electrode layer, the first stiffening layer,
and the second stiffening layer can form a first mechanical layer in the
first region. Forming the movable electrode layer can further include
forming the movable electrode layer on the second stiffening layer in the
second region. The movable electrode layer and the second stiffening
layer can form a second mechanical layer in the second region. Forming
the movable electrode layer can further include forming the movable
electrode layer on the third sacrificial layer in the third region. The
movable electrode layer can form a third mechanical layer in the third
region.

[0010] Another innovative aspect can be implemented in an
electromechanical system including at least a first electromechanical
device and a second electromechanical device. The electromechanical
system further includes means for supporting the first and second
electromechanical devices, means for defining a first gap for the first
electromechanical device, and means for defining a second gap for the
second electromechanical device. The second gap has a different size than
the first gap. The system further includes means for selectively
collapsing and opening the first gap for the first electromechanical
device, means for selectively collapsing and opening the second gap for
the second electromechanical device, and first stiffening means for
stiffening the means for selectively collapsing and opening the first
gap. The first stiffening means faces the first gap. The system further
includes second stiffening means for stiffening the means for selectively
collapsing and opening the second gap. The second stiffening means faces
the second gap and provides a different stiffness from the first
stiffening means.

[0011] In some implementations, the electromechanical system can further
include a first etch stop means on the first electrode of the means for
selectively collapsing and opening the first gap and a second etch stop
means on the first electrode of the means for selectively collapsing and
opening the second gap. The first electrode of the means for selectively
collapsing and opening the first gap can be positioned under the second
electrode of the means for selectively collapsing and opening the first
gap. The first electrode of the means for selectively collapsing and
opening the second gap can be positioned under the second electrode of
the means for selectively collapsing and opening the second gap.

[0012] Details of one or more implementations of the subject matter
described in this specification are set forth in the accompanying
drawings and the description below. Other features, aspects, and
advantages will become apparent from the description, the drawings, and
the claims. Note that the relative dimensions of the following figures
may not be drawn to scale.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 shows an example of an isometric view depicting two adjacent
pixels in a series of pixels of an interferometric modulator (IMOD)
display device.

[0015]FIG. 3A shows an example of a diagram illustrating movable
reflective layer position versus applied voltage for the interferometric
modulator of FIG. 1.

[0016]FIG. 3B shows an example of a table illustrating various states of
an interferometric modulator when various common and segment voltages are
applied.

[0017]FIG. 4A shows an example of a diagram illustrating a frame of
display data in the 3×3 interferometric modulator display of FIG.
2.

[0018]FIG. 4B shows an example of a timing diagram for common and segment
signals that may be used to write the frame of display data illustrated
in FIG. 4A.

[0019]FIG. 5A shows an example of a partial cross-section of the
interferometric modulator display of FIG. 1.

[0020] FIGS. 5B-5E show examples of cross-sections of varying
implementations of interferometric modulators.

[0021]FIG. 6 shows an example of a flow diagram illustrating a
manufacturing process for an interferometric modulator.

[0022] FIGS. 7A-7E show examples of cross-sectional schematic
illustrations of various stages in a method of making an interferometric
modulator.

[0023] FIG. 8A shows an example of a schematic cross-section of three
different electromechanical device types with all three shown in the open
state having different sized air gaps and stiffening layers of different
thickness.

[0024] FIG. 8B shows an example of a schematic cross-section of the
devices of FIG. 8A in the collapsed state.

[0025] FIGS. 9A-9H show examples of schematic cross-sections illustrating
an electromechanical device fabrication process including etch stops that
remain as part of the electromechanical device.

[0026]FIG. 10A shows an example of a schematic cross-section of two
different electromechanical device types with both shown in the open
state having different sized air gaps and stiffening layers of different
thickness.

[0027] FIG. 10B shows an example of a schematic cross-section of the
devices of FIG. 10A in the collapsed state.

[0028] FIGS. 11A-11F show examples of schematic cross-sections
illustrating an electromechanical device fabrication process including
etch stops that remain as part of the electromechanical device, for two
different electromechanical device types.

[0029]FIG. 12 shows an example of a flow chart illustrating a process of
fabricating different electromechanical device types with different
sacrificial layer thicknesses.

[0030] FIGS. 13A and 13B show examples of system block diagrams
illustrating a display device that includes a plurality of
interferometric modulators.

[0031] Like reference numbers and designations in the various drawings
indicate like elements.

DETAILED DESCRIPTION

[0032] The following detailed description is directed to certain
implementations for the purposes of describing the innovative aspects.
However, the teachings herein can be applied in a multitude of different
ways. The described implementations may be implemented in any device that
is configured to display an image, whether in motion (e.g., video) or
stationary (e.g., still image), and whether textual, graphical or
pictorial. More particularly, it is contemplated that the implementations
may be implemented in or associated with a variety of electronic devices
such as, but not limited to, mobile telephones, multimedia Internet
enabled cellular telephones, mobile television receivers, wireless
devices, smartphones, bluetooth devices, personal data assistants (PDAs),
wireless electronic mail receivers, hand-held or portable computers,
netbooks, notebooks, smartbooks, printers, copiers, scanners, facsimile
devices, GPS receivers/navigators, cameras, MP3 players, camcorders, game
consoles, wrist watches, clocks, calculators, television monitors, flat
panel displays, electronic reading devices (e.g., e-readers), computer
monitors, auto displays (e.g., odometer display, etc.), cockpit controls
and/or displays, camera view displays (e.g., display of a rear view
camera in a vehicle), electronic photographs, electronic billboards or
signs, projectors, architectural structures, microwaves, refrigerators,
stereo systems, cassette recorders or players, DVD players, CD players,
VCRs, radios, portable memory chips, washers, dryers, washer/dryers,
packaging (e.g., MEMS and non-MEMS), aesthetic structures (e.g., display
of images on a piece of jewelry) and a variety of electromechanical
systems devices. The teachings herein also can be used in non-display
applications such as, but not limited to, electronic switching devices,
radio frequency filters, sensors, accelerometers, gyroscopes,
motion-sensing devices, magnetometers, inertial components for consumer
electronics, parts of consumer electronics products, varactors, liquid
crystal devices, electrophoretic devices, drive schemes, manufacturing
processes, electronic test equipment. Thus, the teachings are not
intended to be limited to the implementations depicted solely in the
Figures, but instead have wide applicability as will be readily apparent
to a person having ordinary skill in the art.

[0033] An array of electromechanical systems devices can be implemented to
have at least two different electromechanical device types, such as
different interferometric modulator types corresponding to different
reflected colors. Each different device type can have a different sized
air gap. Each different device type can have a mechanical sub-layer with
a different thickness. The mechanical sub-layers can be deposited for use
as etch stops for patterning sacrificial layers to define the different
air gaps, and can remain as part of a movable electrode after removal of
the sacrificial layers.

[0034] Particular implementations of the subject matter described in this
disclosure can be implemented to realize one or more of the following
potential advantages. The different thicknesses of the mechanical
sub-layer can allow an array of electromechanical systems devices to use
a normalized actuation voltage. Normalization of the actuation voltage
can reduce the complexity, and therefore the cost, of driving circuitry.
Furthermore, an array of electromechanical systems devices as described
herein can be constructed with minimal masking processes. Multiple masks
may be employed to define the different sacrificial layer thicknesses
that ultimately result in different electromechanical systems device gap
sizes. However, the processes described here allow simultaneous
definition of multiple mechanical layer thicknesses without additional
mask processes. Using fewer masks can further reduce the cost of
production and increase yield.

[0035] One example of a suitable electromechanical systems device, e.g., a
MEMS device, to which the described implementations may apply, is a
reflective display device. Reflective display devices can incorporate
interferometric modulators (IMODs) to selectively absorb and/or reflect
light incident thereon using principles of optical interference. IMODs
can include an absorber, a reflector that is movable with respect to the
absorber, and an optical resonant cavity defined between the absorber and
the reflector. The reflector can be moved to two or more different
positions, which can change the size of the optical resonant cavity and
thereby affect the reflectance of the interferometric modulator. The
reflectance spectrums of IMODs can create fairly broad spectral bands
which can be shifted across the visible wavelengths to generate different
colors. The position of the spectral band can be adjusted by changing the
thickness of the optical resonant cavity, i.e., by changing the position
of the reflector.

[0036]FIG. 1 shows an example of an isometric view depicting two adjacent
pixels in a series of pixels of an interferometric modulator (IMOD)
display device. The IMOD display device includes one or more
interferometric MEMS display elements. In these devices, the pixels of
the MEMS display elements can be in either a bright or dark state. In the
bright ("relaxed," "open" or "on") state, the display element reflects a
large portion of incident visible light, e.g., to a user. Conversely, in
the dark ("actuated," "closed" or "off") state, the display element
reflects little incident visible light. In some implementations, the
light reflectance properties of the on and off states may be reversed.
MEMS pixels can be configured to reflect predominantly at particular
wavelengths, allowing for a color display in addition to black and white.

[0037] The IMOD display device can include a row/column array of IMODs.
Each IMOD can include a pair of reflective layers, particularly a movable
reflective layer and a fixed partially reflective layer, positioned at a
variable and controllable distance from each other to form an air gap
(also referred to as an optical gap or cavity). The movable reflective
layer may be moved between at least two positions. In a first position,
i.e., a relaxed position, the movable reflective layer can be positioned
at a relatively large distance from the fixed partially reflective layer.
In a second position, i.e., an actuated position, the movable reflective
layer can be positioned more closely to the partially reflective layer.
Incident light that reflects from the two layers can interfere
constructively or destructively depending on the position of the movable
reflective layer, producing either an overall reflective or
non-reflective state for each pixel. In some implementations, the IMOD
may be in a reflective state when unactuated, reflecting light within the
visible spectrum, and may be in a dark state when unactuated, reflecting
light outside of the visible range (e.g., infrared light). In some other
implementations, however, an IMOD may be in a dark state when unactuated,
and in a reflective state when actuated. In some implementations, the
introduction of an applied voltage can drive the pixels to change states.
In some other implementations, an applied charge can drive the pixels to
change states.

[0038] The depicted portion of the pixel array in FIG. 1 includes two
adjacent interferometric modulators 12. In the IMOD 12 on the left (as
illustrated), a movable reflective layer 14 is illustrated in a relaxed
position at a predetermined distance from an optical stack 16, which
includes a partially reflective layer. The voltage V0 applied across
the IMOD 12 on the left is insufficient to cause actuation of the movable
reflective layer 14. In the IMOD 12 on the right, the movable reflective
layer 14 is illustrated in an actuated position near or adjacent the
optical stack 16, which serves as or includes the stationary electrode
for the illustrated IMOD implementation. The voltage Vbias applied
across the IMOD 12 on the right is sufficient to maintain the movable
reflective layer 14 in the actuated position.

[0039] In FIG. 1, the reflective properties of pixels 12 are generally
illustrated with arrows 13 indicating light incident upon the pixels 12,
and light 15 reflecting from the pixel 12 on the left. Although not
illustrated in detail, it will be understood by a person having ordinary
skill in the art that most of the light 13 incident upon the pixels 12
will be transmitted through the transparent substrate 20, toward the
optical stack 16. A portion of the light incident upon the optical stack
16 will be transmitted through the partially reflective layer of the
optical stack 16, and a portion will be reflected back through the
transparent substrate 20. The portion of light 13 that is transmitted
through the optical stack 16 will be reflected at the movable reflective
layer 14 back toward (and through) the transparent substrate 20.
Interference (constructive or destructive) between the light reflected
from the partially reflective layer of the optical stack 16 and the light
reflected from the movable reflective layer 14 will determine the
wavelength(s) of light 15 reflected from the pixel 12.

[0040] The optical stack 16 can include a single layer or several layers.
The layer(s) can include one or more of an electrode layer, a partially
reflective and partially transmissive layer and a transparent dielectric
layer. In some implementations, the optical stack 16 is electrically
conductive, partially transparent and partially reflective, and may be
fabricated, for example, by depositing one or more of the above layers
onto a transparent substrate 20. The electrode layer can be formed from a
variety of materials, such as various metals, for example indium tin
oxide (ITO). The partially reflective layer can be formed from a variety
of materials that are partially reflective, such as various metals, e.g.,
chromium (Cr), semiconductors, and dielectrics. The partially reflective
layer can be formed of one or more layers of materials, and each of the
layers can be formed of a single material or a combination of materials.
In some implementations, the optical stack 16 can include a single
semi-transparent thickness of metal or semiconductor which serves as both
an optical absorber and conductor, while different, more conductive
layers or portions (e.g., of the optical stack 16 or of other structures
of the IMOD) can serve to bus signals between IMOD pixels. The optical
stack 16 also can include one or more insulating or dielectric layers
covering one or more conductive layers or a conductive/absorptive layer.

[0041] In some implementations, the layer(s) of the optical stack 16 can
be patterned into parallel strips, and may form row electrodes in a
display device as described further below. As will be understood by a
person having ordinary skill in the art, the term "patterned" is used
herein to refer to masking as well as etching processes. In some
implementations, a highly conductive and reflective material, such as
aluminum (Al), may be used for the movable reflective layer 14, and these
strips may form column electrodes in a display device. The movable
reflective layer 14 may be formed as a series of parallel strips of a
deposited metal layer or layers (orthogonal to the row electrodes of the
optical stack 16) to form columns deposited on top of posts 18 and an
intervening sacrificial material deposited between the posts 18. When the
sacrificial material is etched away, a defined gap 19, or optical cavity,
can be formed between the movable reflective layer 14 and the optical
stack 16. In some implementations, the spacing between posts 18 may be on
the order of 1-1000 microns (μm), while the gap 19 may be on the order
of <10,000 Angstroms (Å).

[0042] In some implementations, each pixel of the IMOD, whether in the
actuated or relaxed state, is essentially a capacitor formed by the fixed
and moving reflective layers. When no voltage is applied, the movable
reflective layer 14 remains in a mechanically relaxed state, as
illustrated by the pixel 12 on the left in FIG. 1, with the gap 19
between the movable reflective layer 14 and optical stack 16. However,
when a potential difference, e.g., voltage, is applied to at least one of
a selected row and column, the capacitor formed at the intersection of
the row and column electrodes at the corresponding pixel becomes charged,
and electrostatic forces pull the electrodes together. If the applied
voltage exceeds a threshold, the movable reflective layer 14 can deform
and move near or against the optical stack 16. A dielectric layer (not
shown) within the optical stack 16 may prevent shorting and control the
separation distance between the layers 14 and 16, as illustrated by the
actuated pixel 12 on the right in FIG. 1. The behavior is the same
regardless of the polarity of the applied potential difference. Though a
series of pixels in an array may be referred to in some instances as
"rows" or "columns," a person having ordinary skill in the art will
readily understand that referring to one direction as a "row" and another
as a "column" is arbitrary. Restated, in some orientations, the rows can
be considered columns, and the columns considered to be rows.
Furthermore, the display elements may be evenly arranged in orthogonal
rows and columns (an "array"), or arranged in non-linear configurations,
for example, having certain positional offsets with respect to one
another (a "mosaic"). The terms "array" and "mosaic" may refer to either
configuration. Thus, although the display is referred to as including an
"array" or "mosaic," the elements themselves need not be arranged
orthogonally to one another, or disposed in an even distribution, in any
instance, but may include arrangements having asymmetric shapes and
unevenly distributed elements.

[0043] FIG. 2 shows an example of a system block diagram illustrating an
electronic device incorporating a 3×3 interferometric modulator
display. The electronic device includes a processor 21 that may be
configured to execute one or more software modules. In addition to
executing an operating system, the processor 21 may be configured to
execute one or more software applications, including a web browser, a
telephone application, an email program, or any other software
application.

[0044] The processor 21 can be configured to communicate with an array
driver 22. The array driver 22 can include a row driver circuit 24 and a
column driver circuit 26 that provide signals to, e.g., a display array
or panel 30. The cross section of the IMOD display device illustrated in
FIG. 1 is shown by the lines 1-1 in FIG. 2. Although FIG. 2 illustrates a
3×3 array of IMODs for the sake of clarity, the display array 30
may contain a very large number of IMODs, and may have a different number
of IMODs in rows than in columns, and vice versa.

[0045]FIG. 3A shows an example of a diagram illustrating movable
reflective layer position versus applied voltage for the interferometric
modulator of FIG. 1. For MEMS interferometric modulators, the row/column
(i.e., common/segment) write procedure may take advantage of a hysteresis
property of these devices as illustrated in FIG. 3A. An interferometric
modulator may require, for example, about a 10-volt potential difference
to cause the movable reflective layer, or mirror, to change from the
relaxed state to the actuated state. When the voltage is reduced from
that value, the movable reflective layer maintains its state as the
voltage drops back below, e.g., 10-volts; however, the movable reflective
layer does not relax completely until the voltage drops below 2-volts.
Thus, a range of voltage, approximately 3 to 7-volts, as shown in FIG.
3A, exists where there is a window of applied voltage within which the
device is stable in either the relaxed or actuated state. This is
referred to herein as the "hysteresis window" or "stability window." For
a display array 30 having the hysteresis characteristics of FIG. 3A, the
row/column write procedure can be designed to address one or more rows at
a time, such that during the addressing of a given row, pixels in the
addressed row that are to be actuated are exposed to a voltage difference
of about 10-volts, and pixels that are to be relaxed are exposed to a
voltage difference of near zero volts. After addressing, the pixels are
exposed to a steady state or bias voltage difference of approximately
5-volts such that they remain in the previous strobing state. In this
example, after being addressed, each pixel sees a potential difference
within the "stability window" of about 3-7-volts. This hysteresis
property feature enables the pixel design, e.g., illustrated in FIG. 1,
to remain stable in either an actuated or relaxed pre-existing state
under the same applied voltage conditions. Since each IMOD pixel, whether
in the actuated or relaxed state, is essentially a capacitor formed by
the fixed and moving reflective layers, this stable state can be held at
a steady voltage within the hysteresis window without substantially
consuming or losing power. Moreover, essentially little or no current
flows into the IMOD pixel if the applied voltage potential remains
substantially fixed.

[0046] In some implementations, a frame of an image may be created by
applying data signals in the form of "segment" voltages along the set of
column electrodes, in accordance with the desired change (if any) to the
state of the pixels in a given row. Each row of the array can be
addressed in turn, such that the frame is written one row at a time. To
write the desired data to the pixels in a first row, segment voltages
corresponding to the desired state of the pixels in the first row can be
applied on the column electrodes, and a first row pulse in the form of a
specific "common" voltage or signal can be applied to the first row
electrode. The set of segment voltages can then be changed to correspond
to the desired change (if any) to the state of the pixels in the second
row, and a second common voltage can be applied to the second row
electrode. In some implementations, the pixels in the first row are
unaffected by the change in the segment voltages applied along the column
electrodes, and remain in the state they were set to during the first
common voltage row pulse. This process may be repeated for the entire
series of rows, or alternatively, columns, in a sequential fashion to
produce the image frame. The frames can be refreshed and/or updated with
new image data by continually repeating this process at some desired
number of frames per second.

[0047] The combination of segment and common signals applied across each
pixel (that is, the potential difference across each pixel) determines
the resulting state of each pixel. FIG. 3B shows an example of a table
illustrating various states of an interferometric modulator when various
common and segment voltages are applied. As will be readily understood by
a person having ordinary skill in the art, the "segment" voltages can be
applied to either the column electrodes or the row electrodes, and the
"common" voltages can be applied to the other of the column electrodes or
the row electrodes.

[0048] As illustrated in FIG. 3B (as well as in the timing diagram shown
in FIG. 4B), when a release voltage VCREL is applied along a common
line, all interferometric modulator elements along the common line will
be placed in a relaxed state, alternatively referred to as a released or
unactuated state, regardless of the voltage applied along the segment
lines, i.e., high segment voltage VSH and low segment voltage
VSL. In particular, when the release voltage VCREL is applied
along a common line, the potential voltage across the modulator
(alternatively referred to as a pixel voltage) is within the relaxation
window (see FIG. 3A, also referred to as a release window) both when the
high segment voltage VSH and the low segment voltage VSL are
applied along the corresponding segment line for that pixel.

[0049] When a hold voltage is applied on a common line, such as a high
hold voltage VCHOLD--H or a low hold voltage
VCHOLD--L, the state of the interferometric modulator will
remain constant. For example, a relaxed IMOD will remain in a relaxed
position, and an actuated IMOD will remain in an actuated position. The
hold voltages can be selected such that the pixel voltage will remain
within a stability window both when the high segment voltage VSH and
the low segment voltage VSL are applied along the corresponding
segment line. Thus, the segment voltage swing, i.e., the difference
between the high VSH and low segment voltage VSL, is less than
the width of either the positive or the negative stability window.

[0050] When an addressing, or actuation, voltage is applied on a common
line, such as a high addressing voltage VCADD--H or a low
addressing voltage VCADD--L, data can be selectively
written to the modulators along that line by application of segment
voltages along the respective segment lines. The segment voltages may be
selected such that actuation is dependent upon the segment voltage
applied. When an addressing voltage is applied along a common line,
application of one segment voltage will result in a pixel voltage within
a stability window, causing the pixel to remain unactuated. In contrast,
application of the other segment voltage will result in a pixel voltage
beyond the stability window, resulting in actuation of the pixel. The
particular segment voltage which causes actuation can vary depending upon
which addressing voltage is used. In some implementations, when the high
addressing voltage VCADD--H is applied along the common
line, application of the high segment voltage VSH can cause a
modulator to remain in its current position, while application of the low
segment voltage VSL can cause actuation of the modulator. As a
corollary, the effect of the segment voltages can be the opposite when a
low addressing voltage VCADD--L is applied, with high
segment voltage VSH causing actuation of the modulator, and low
segment voltage VSL having no effect (i.e., remaining stable) on the
state of the modulator.

[0051] In some implementations, hold voltages, address voltages, and
segment voltages may be used which always produce the same polarity
potential difference across the modulators. In some other
implementations, signals can be used which alternate the polarity of the
potential difference of the modulators. Alternation of the polarity
across the modulators (that is, alternation of the polarity of write
procedures) may reduce or inhibit charge accumulation which could occur
after repeated write operations of a single polarity.

[0052]FIG. 4A shows an example of a diagram illustrating a frame of
display data in the 3×3 interferometric modulator display of FIG.
2. FIG. 4B shows an example of a timing diagram for common and segment
signals that may be used to write the frame of display data illustrated
in FIG. 4A. The signals can be applied to the, e.g., 3×3 array of
FIG. 2, which will ultimately result in the line time 60e display
arrangement illustrated in FIG. 4A. The actuated modulators in FIG. 4A
are in a dark-state, i.e., where a substantial portion of the reflected
light is outside of the visible spectrum so as to result in a dark
appearance to, e.g., a viewer. Prior to writing the frame illustrated in
FIG. 4A, the pixels can be in any state, but the write procedure
illustrated in the timing diagram of FIG. 4B presumes that each modulator
has been released and resides in an unactuated state before the first
line time 60a.

[0053] During the first line time 60a: a release voltage 70 is applied on
common line 1; the voltage applied on common line 2 begins at a high hold
voltage 72 and moves to a release voltage 70; and a low hold voltage 76
is applied along common line 3. Thus, the modulators (common 1, segment
1), (1,2) and (1,3) along common line 1 remain in a relaxed, or
unactuated, state for the duration of the first line time 60a, the
modulators (2,1), (2,2) and (2,3) along common line 2 will move to a
relaxed state, and the modulators (3,1), (3,2) and (3,3) along common
line 3 will remain in their previous state. With reference to FIG. 3B,
the segment voltages applied along segment lines 1, 2 and 3 will have no
effect on the state of the interferometric modulators, as none of common
lines 1, 2 or 3 are being exposed to voltage levels causing actuation
during line time 60a (i.e., VCREL--relax and
VCHOLD--L--stable).

[0054] During the second line time 60b, the voltage on common line 1 moves
to a high hold voltage 72, and all modulators along common line 1 remain
in a relaxed state regardless of the segment voltage applied because no
addressing, or actuation, voltage was applied on the common line 1. The
modulators along common line 2 remain in a relaxed state due to the
application of the release voltage 70, and the modulators (3,1), (3,2)
and (3,3) along common line 3 will relax when the voltage along common
line 3 moves to a release voltage 70.

[0055] During the third line time 60c, common line 1 is addressed by
applying a high address voltage 74 on common line 1. Because a low
segment voltage 64 is applied along segment lines 1 and 2 during the
application of this address voltage, the pixel voltage across modulators
(1,1) and (1,2) is greater than the high end of the positive stability
window (i.e., the voltage differential exceeded a predefined threshold)
of the modulators, and the modulators (1,1) and (1,2) are actuated.
Conversely, because a high segment voltage 62 is applied along segment
line 3, the pixel voltage across modulator (1,3) is less than that of
modulators (1,1) and (1,2), and remains within the positive stability
window of the modulator; modulator (1,3) thus remains relaxed. Also
during line time 60c, the voltage along common line 2 decreases to a low
hold voltage 76, and the voltage along common line 3 remains at a release
voltage 70, leaving the modulators along common lines 2 and 3 in a
relaxed position.

[0056] During the fourth line time 60d, the voltage on common line 1
returns to a high hold voltage 72, leaving the modulators along common
line 1 in their respective addressed states. The voltage on common line 2
is decreased to a low address voltage 78. Because a high segment voltage
62 is applied along segment line 2, the pixel voltage across modulator
(2,2) is below the lower end of the negative stability window of the
modulator, causing the modulator (2,2) to actuate. Conversely, because a
low segment voltage 64 is applied along segment lines 1 and 3, the
modulators (2,1) and (2,3) remain in a relaxed position. The voltage on
common line 3 increases to a high hold voltage 72, leaving the modulators
along common line 3 in a relaxed state.

[0057] Finally, during the fifth line time 60e, the voltage on common line
1 remains at high hold voltage 72, and the voltage on common line 2
remains at a low hold voltage 76, leaving the modulators along common
lines 1 and 2 in their respective addressed states. The voltage on common
line 3 increases to a high address voltage 74 to address the modulators
along common line 3. As a low segment voltage 64 is applied on segment
lines 2 and 3, the modulators (3,2) and (3,3) actuate, while the high
segment voltage 62 applied along segment line 1 causes modulator (3,1) to
remain in a relaxed position. Thus, at the end of the fifth line time
60e, the 3×3 pixel array is in the state shown in FIG. 4A, and will
remain in that state as long as the hold voltages are applied along the
common lines, regardless of variations in the segment voltage which may
occur when modulators along other common lines (not shown) are being
addressed.

[0058] In the timing diagram of FIG. 4B, a given write procedure (e.g.,
line times 60a-60e) can include the use of either high hold and address
voltages, or low hold and address voltages. Once the write procedure has
been completed for a given common line (and the common voltage is set to
the hold voltage having the same polarity as the actuation voltage), the
pixel voltage remains within a given stability window, and does not pass
through the relaxation window until a release voltage is applied on that
common line. Furthermore, as each modulator is released as part of the
write procedure prior to addressing the modulator, the actuation time of
a modulator, rather than the release time, may determine the necessary
line time. Specifically, in implementations in which the release time of
a modulator is greater than the actuation time, the release voltage may
be applied for longer than a single line time, as depicted in FIG. 4B. In
some other implementations, voltages applied along common lines or
segment lines may vary to account for variations in the actuation and
release voltages of different modulators, such as modulators of different
colors.

[0059] The details of the structure of interferometric modulators that
operate in accordance with the principles set forth above may vary
widely. For example, FIGS. 5A-5E show examples of cross-sections of
varying implementations of interferometric modulators, including the
movable reflective layer 14 and its supporting structures. FIG. 5A shows
an example of a partial cross-section of the interferometric modulator
display of FIG. 1, where a strip of metal material, i.e., the movable
reflective layer 14 is deposited on supports 18 extending orthogonally
from the substrate 20. In FIG. 5B, the movable reflective layer 14 of
each IMOD is generally square or rectangular in shape and attached to
supports at or near the corners, on tethers 32. In FIG. 5c, the movable
reflective layer 14 is generally square or rectangular in shape and
suspended from a deformable layer 34, which may include a flexible metal.
The deformable layer 34 can connect, directly or indirectly, to the
substrate 20 around the perimeter of the movable reflective layer 14.
These connections are herein referred to as support posts. The
implementation shown in FIG. 5c has additional benefits deriving from the
decoupling of the optical functions of the movable reflective layer 14
from its mechanical functions, which are carried out by the deformable
layer 34. This decoupling allows the structural design and materials used
for the reflective layer 14 and those used for the deformable layer 34 to
be optimized independently of one another.

[0060]FIG. 5D shows another example of an IMOD, where the movable
reflective layer 14 includes a reflective sub-layer 14a. The movable
reflective layer 14 rests on a support structure, such as support posts
18. The support posts 18 provide separation of the movable reflective
layer 14 from the lower stationary electrode (e.g., part of the optical
stack 16 in the illustrated IMOD) so that a gap 19 is formed between the
movable reflective layer 14 and the optical stack 16, for example when
the movable reflective layer 14 is in a relaxed position. The movable
reflective layer 14 also can include a conductive layer 14c, which may be
configured to serve as an electrode, and a support layer 14b. In this
example, the conductive layer 14c is disposed on one side of the support
layer 14b, distal from the substrate 20, and the reflective sub-layer 14a
is disposed on the other side of the support layer 14b, proximal to the
substrate 20. In some implementations, the reflective sub-layer 14a can
be conductive and can be disposed between the support layer 14b and the
optical stack 16. The support layer 14b can include one or more layers of
a dielectric material, for example, silicon oxynitride (SiON) or silicon
dioxide (SiO2). In some implementations, the support layer 14b can
be a stack of layers, such as, for example, a SiO2/SiON/SiO2
tri-layer stack. Either or both of the reflective sub-layer 14a and the
conductive layer 14c can include, e.g., an Al alloy with about 0.5% Cu,
or another reflective metallic material. Employing conductive layers 14a,
14c above and below the dielectric support layer 14b can balance stresses
and provide enhanced conduction. In some implementations, the reflective
sub-layer 14a and the conductive layer 14c can be formed of different
materials for a variety of design purposes, such as achieving specific
stress profiles within the movable reflective layer 14.

[0061] As illustrated in FIG. 5D, some implementations also can include a
black mask structure 23. The black mask structure 23 can be formed in
optically inactive regions (e.g., between pixels or under posts 18) to
absorb ambient or stray light. The black mask structure 23 also can
improve the optical properties of a display device by inhibiting light
from being reflected from or transmitted through inactive portions of the
display, thereby increasing the contrast ratio. Additionally, the black
mask structure 23 can include conductor(s) and be configured to function
as an electrical bussing layer. In some implementations, the row
electrodes can be connected to the black mask structure 23 to reduce the
resistance of the connected row electrode. The black mask structure 23
can be formed using a variety of methods, including deposition and
patterning techniques. The black mask structure 23 can include one or
more layers. For example, in some implementations, the black mask
structure 23 includes a molybdenum-chromium (MoCr) layer that serves as
an optical absorber, a SiO2 layer, and an aluminum alloy that serves
as a reflector and a bussing layer, with thicknesses in the range of
about 30-80 Å, 500-1000 Å, and 500-6000 Å, respectively. The
one or more layers can be patterned using a variety of techniques,
including photolithography and dry etching, including, for example,
CF4 and/or O2 for the MoCr and SiO2 layers and Cl2
and/or BCl3 for the aluminum alloy layer. In some implementations,
the black mask 23 can be an etalon or interferometric stack structure. In
such interferometric stack black mask structures 23, the conductive
absorbers can be used to transmit or bus signals between lower,
stationary electrodes in the optical stack 16 of each row or column. In
some implementations, a spacer layer 35 can serve to generally
electrically isolate the absorber layer 16a from the conductive layers in
the black mask 23.

[0062]FIG. 5E shows another example of an IMOD, where the movable
reflective layer 14 is self supporting. In contrast with FIG. 5D, the
implementation of FIG. 5E does not include separate materials for the
support posts 18. Instead, at least a portion of the movable reflective
layer 14 contacts the underlying optical stack 16 at multiple locations,
and the curvature of the movable reflective layer 14 provides sufficient
support that the movable reflective layer 14 returns to the unactuated
position of FIG. 5E when the voltage across the interferometric modulator
is insufficient to cause actuation. The optical stack 16, which may
contain a plurality of several different layers, is shown here for
clarity including an optical absorber 16a, and a dielectric 16b. In some
implementations, the optical absorber 16a may serve both as a fixed
electrode and as a partially reflective layer.

[0063] In implementations such as those shown in FIGS. 5A-5E, the IMODs
function as direct-view devices, in which images are viewed from the
front side of the transparent substrate 20, i.e., the side opposite to
that upon which the modulator is arranged. In these implementations, the
back portions of the device (that is, any portion of the display device
behind the movable reflective layer 14, including, for example, the
deformable layer 34 illustrated in FIG. 5c) can be configured and
operated upon without impacting or negatively affecting the image quality
of the display device, because the reflective layer 14 optically shields
those portions of the device. For example, in some implementations a bus
structure (not illustrated) can be included behind the movable reflective
layer 14, which provides the ability to separate the optical properties
of the modulator from the electromechanical properties of the modulator,
such as voltage addressing and the movements that result from such
addressing. Additionally, the implementations of FIGS. 5A-5E can simplify
processing, such as, e.g., patterning.

[0064]FIG. 6 shows an example of a flow diagram illustrating a
manufacturing process 80 for an interferometric modulator, and FIGS.
7A-7E show examples of cross-sectional schematic illustrations of
corresponding stages of such a manufacturing process 80. In some
implementations, the manufacturing process 80 can be implemented to
manufacture, e.g., interferometric modulators of the general type
illustrated in FIGS. 1 and 5A-5E, in addition to other blocks not shown
in FIG. 6. With reference to FIGS. 1, 5A-5E and 6, the process 80 begins
at block 82 with the formation of the optical stack 16 over the substrate
20. FIG. 7A illustrates such an optical stack 16 formed over the
substrate 20. The substrate 20 may be a transparent substrate such as
glass or plastic, it may be flexible or relatively stiff and unbending,
and may have been subjected to prior preparation processes, e.g.,
cleaning, to facilitate efficient formation of the optical stack 16. As
discussed above, the optical stack 16 can be electrically conductive,
partially transparent and partially reflective and may be fabricated, for
example, by depositing one or more layers having the desired properties
onto the transparent substrate 20. In FIG. 7A, the optical stack 16
includes a multilayer structure having sub-layers 16a and 16b, although
more or fewer sub-layers may be included in some other implementations.
In some implementations, one of the sub-layers 16a, 16b can be configured
with both optically absorptive and conductive properties, such as the
combined conductor/absorber sub-layer 16a. Additionally, one or more of
the sub-layers 16a, 16b can be patterned into parallel strips, and may
form row electrodes in a display device. Such patterning can be performed
by a masking and etching process or another suitable process known in the
art. In some implementations, one of the sub-layers 16a, 16b can be an
insulating or dielectric layer, such as sub-layer 16b that is deposited
over one or more metal layers (e.g., one or more reflective and/or
conductive layers). In addition, the optical stack 16 can be patterned
into individual and parallel strips that form the rows of the display.

[0065] The process 80 continues at block 84 with the formation of a
sacrificial layer 25 over the optical stack 16. The sacrificial layer 25
is later removed (e.g., at block 90) to form the cavity 19 (FIG. 7E) and
thus the sacrificial layer 25 is not shown in the resulting
interferometric modulators 12 illustrated in FIG. 1. FIG. 7B illustrates
a partially fabricated device including a sacrificial layer 25 formed
over the optical stack 16. The formation of the sacrificial layer 25 over
the optical stack 16 may include deposition of a fluorine-etchable
material such as molybdenum (Mo) or amorphous silicon (Si), in a
thickness selected to provide, after subsequent removal, a gap or cavity
19 (see also FIGS. 1 and 7E) having a desired design size. Deposition of
the sacrificial material may be carried out using deposition techniques
such as physical vapor deposition (PVD, e.g., sputtering),
plasma-enhanced chemical vapor deposition (PECVD), thermal chemical vapor
deposition (thermal CVD), or spin-coating.

[0066] The process 80 continues at block 86 with the formation of a
support structure e.g., a post 18 as illustrated in FIGS. 1, 5A-5E and
7C. The formation of the post 18 may include patterning the sacrificial
layer 25 to form a support structure aperture, then depositing a material
(e.g., a polymer or an inorganic material, e.g., silicon oxide) into the
aperture to form the post 18, using a deposition method such as PVD,
PECVD, thermal CVD, or spin-coating. In some implementations, the support
structure aperture formed in the sacrificial layer can extend through
both the sacrificial layer 25 and the optical stack 16 to the underlying
substrate 20, so that the lower end of the post 18 contacts the substrate
20 as illustrated in FIG. 5A. Alternatively, as depicted in FIG. 7C, the
aperture formed in the sacrificial layer 25 can extend through the
sacrificial layer 25, but not through the optical stack 16. For example,
FIG. 7E illustrates the lower ends of the support posts 18 in contact
with an upper surface of the optical stack 16. In other arrangements, the
support posts can land on a black mask structure. The post 18, or other
support structures, may be formed by depositing a layer of support
structure material over the sacrificial layer 25 and patterning portions
of the support structure material located away from apertures in the
sacrificial layer 25. The support structures may be located within the
apertures, as illustrated in FIG. 7C, but also can, at least partially,
extend over a portion of the sacrificial layer 25. As noted above, the
patterning of the sacrificial layer 25 and/or the support posts 18 can be
performed by masking and etching processes, but also may be performed by
alternative patterning methods.

[0067] The process 80 continues at block 88 with the formation of a
movable reflective layer or membrane such as the movable reflective layer
14 illustrated in FIGS. 1, 5A-5E and 7D. The movable reflective layer 14
may be formed by employing one or more depositions, e.g., reflective
layer (e.g., aluminum, aluminum alloy) deposition, along with one or more
patterning, masking, and/or etching processes. The movable reflective
layer 14 can be electrically conductive, and referred to as an
electrically conductive layer. In some implementations, the movable
reflective layer 14 may include a plurality of sub-layers 14a, 14b, 14c
as shown in FIG. 7D. In some implementations, one or more of the
sub-layers, such as sub-layers 14a, 14c, may include highly reflective
sub-layers selected for their optical properties, and another sub-layer
14b may include a mechanical sub-layer selected for its mechanical
properties. Since the sacrificial layer 25 is still present in the
partially fabricated interferometric modulator formed at block 88, the
movable reflective layer 14 is typically not movable at this stage. A
partially fabricated IMOD that contains a sacrificial layer 25 may also
be referred to herein as an "unreleased" IMOD. As described above in
connection with FIG. 1, the movable reflective layer 14 can be patterned
into individual and parallel strips that form the columns of the display.

[0068] The process 80 continues at block 90 with the formation of a
cavity, e.g., cavity 19 as illustrated in FIGS. 1, 5 and 7E. The cavity
19 may be formed by exposing the sacrificial material 25 (deposited at
block 84) to an etchant. For example, an etchable sacrificial material
such as Mo or amorphous Si may be removed by dry chemical etching, e.g.,
by exposing the sacrificial layer 25 to a gaseous or vaporous etchant,
such as vapors derived from solid XeF2 for a period of time that is
effective to remove the desired amount of material, typically selectively
removed relative to the structures surrounding the cavity 19. Other
etching methods, e.g. wet etching and/or plasma etching, also may be
used. Since the sacrificial layer 25 is removed during block 90, the
movable reflective layer 14 is typically movable after this stage. After
removal of the sacrificial material 25, the resulting fully or partially
fabricated IMOD may be referred to herein as a "released" IMOD.

[0069] The illustrated electromechanical systems devices are optical MEMS
devices referred to as interferometric modulators (IMODs). IMODs may be
manufactured using manufacturing techniques known in the art for making
electromechanical devices. For example, the various material layers
making up the IMODs may be sequentially deposited onto a transparent
substrate with appropriate patterning and etching processes conducted
between depositions. In some implementations, multiple layers may be
deposited during manufacturing without patterning between the
depositions. For example, the movable reflective layer described above
may include a composite structure having two or more layers. While
illustrated in the context of optical electromechanical devices,
particularly IMODs, a skilled artisan will readily appreciate that the
concepts of this disclosure can be applicable to other electromechanical
devices, such as RF switches, gyroscopes, varactors, etc. The principles
and advantages of the structures and sequences described for FIGS. 8A-9H
are readily applicable to non-optical electromechanical systems devices,
particularly for arrays with multiple gap sizes.

[0070] Color interferometric modulator (IMOD) display systems typically
involve arrays of electromechanical devices, in which each
electromechanical device has one of two or more different air gap sizes
where each air gap size can display a color. In one implementation, each
of three different air gap sizes can display red, green, and blue,
respectively. In particular, an electromechanical pixel represents a
pixel in a color display, where each pixel typically includes three IMOD
types or subpixels. Hereinafter, certain implementation examples will be
described for different interferometric electromechanical architectures.

[0071] FIGS. 8A and 8B illustrate one implementation of an
electromechanical device array having three different electromechanical
device types, each with a different gap size. FIG. 8A illustrates the
devices in the open state, while FIG. 8B illustrates the devices in the
collapsed state. While it is possible for electromechanical devices to
have more than two states with differing gap sizes in the different
states, the presently described implementations assume two-state devices,
fully open or fully closed, such that references to "gap size" herein
refer to the maximum gap size in the fully open state.

[0072] FIG. 8A shows an example of a schematic cross-section of three
different electromechanical device types with all three shown in the open
state having different sized air gaps and stiffening layers of different
thickness. In the illustrated implementation, an electromechanical system
device includes a substrate 800 on which at least three different types
of electromechanical systems device structures are formed. In one
implementation, each of the at least three different types of
electromechanical structures can be IMOD devices configured to reflect a
different color in one of the states. The different electromechanical
device types each include a stationary electrode 816. The stationary
electrode 816 is formed on the substrate 800 and may not be of a uniform
thickness between electromechanical structures of different types. In an
IMOD implementation, the stationary electrode 816 can form part of an
optical stack, as described above, and the movable electrodes 850a and
850b can each include a primary mechanical layer 860 and a mechanical
sub-layer 870a and 870b, respectively. In an IMOD implementation, the
mechanical layers 860 can include a movable reflective layer (not shown).
Each of the at least three different types of electromechanical
structures can have a mechanical sub-layer 870 of different thickness. In
the illustrated implementation, the mechanical sub-layer is absent from
one type of electromechanical structure. As mentioned above, the
electromechanical structures include the movable electrodes 850a, 850b
and 850c above the stationary electrode 816, and also include the air
gaps 840a, 840b and 840c formed between the movable electrodes 850a, 850b
and 850c and the stationary electrode 816. A person having ordinary skill
in the art will readily understand that the figures are simplified
schematics and additional layers, such as underlying or intervening
buffer layers, black mask layers, and bussing layers, may be present.

[0073] The movable electrodes 850a, 850b and 850c can be configured to
serve as the moving or upper electrodes for the electromechanical
devices, and can take any of a number of forms (see, e.g., FIGS. 5A-5E).
The stationary electrode 816 can include one or more conductors and can
serve as the lower electrode of the electromechanical device. The
stationary electrode 816 can be patterned in rows that cross with columns
formed by mechanical layer strips to electrically address different
electromechanical devices (e.g., pixels) in an array.

[0074] In FIG. 8A, the electromechanical system includes three
electromechanical structures each having different sized air gaps 840a,
840b and 840c. The air gaps 840a, 840b and 840c can be formed by
depositing sacrificial material between the upper and lower electrodes,
and subsequent removal of the sacrificial material from between the
electrodes by "release" etching. A vapor phase etchant for the release
can be a fluorine-based etchant, such as XeF2, and the sacrificial
layer may be formed, e.g., of Mo, amorphous Si, W, or Ti for selective
removal by F-based etchants relative to surrounding structural materials.
For example, the sacrificial layer can be removed using H2SiF6
as an etchant.

[0075] Furthermore, the movable electrodes 850a, 850b and 850c can vary in
size between the three different electromechanical device types. The
difference in size between the movable electrodes 850a, 850b and 850c can
be due to a difference in thickness of the mechanical sub-layers 870a and
870b. The absence of a mechanical sub-layer constitutes a thickness of
zero for the purpose of distinguishing between different device types.
The difference in thickness among the movable electrodes 850a, 850b and
850c can cause the movable electrodes 850a, 850b and 850c to have
different stiffnesses. In the illustrated implementation, the different
thicknesses of the movable electrodes 850a, 850b and 850c inversely
corresponds to the sizes of the air gaps 840a, 840b and 840c. Because
devices with relatively larger air gaps, such as the air gap 840c, deform
farther in order to transition to the collapsed state, a greater
actuation voltage may be appropriate. By varying the thickness of the
movable electrodes 850a, 850b and 850c such that devices with a larger
air gap 840a, 840b and 840c have a relatively lower stiffness, the
actuation voltages appropriate for transitioning the devices into the
collapsed state can be normalized. This effect can allow an
electromechanical device driver to use the same voltages to collapse or
relax (e.g., with bias) different electromechanical device types having
different air gap sizes.

[0076] FIG. 8B shows an example of a schematic cross-section of the
devices of FIG. 8A in the collapsed state. As shown in the illustrated
implementation, air gaps 840a, 840b and 840c are no longer present when
the electromechanical devices are in the collapsed or actuated state.
While all three electromechanical device types are shown in the collapsed
state, a person having ordinary skill in the art will readily understand
that the air gaps 840a, 840b and 840c can be independently opened and
collapsed in any combination.

[0077] Typically, electromechanical systems device structures use multiple
sacrificial layers with different thicknesses and/or complex masking
sequences to produce multiple air gap sizes. Some exemplary methods of
fabricating air gaps of different sizes are described in U.S. Pat. No.
7,297,471 and U.S. Pat. Pub. No. 2007/0269748. A person having ordinary
skill in the art will readily appreciate that producing air gap layers of
different sizes requires multiple depositions, multiple masks, and
multiple etchings, and that multiple patterning processes increase costs
and give rise to etch attack issues. However, the number of patterning
processes can be reduced by sequencing the deposition of sacrificial
layers and use of etch stop layers. Furthermore, processes described
herein allow the etch stop layers to ultimately become part of the
movable electrode, the stationary electrode, or both. Etch stop layers
that ultimately become part of the electromechanical device can be
referred to generally as solid layers or stiffening layers. The sequence
in which multiple solid layers are used can cause the thicknesses of the
movable electrode to vary between the two or more electromechanical
devices. Because each solid layer can be used both as an etch stop during
processing of sacrificial layers and as part of the movable electrode in
the final device, serving the additional function of providing different
mechanical layer stiffnesses for different device types, fewer total
processes are needed. For example, the process of making three different
sacrificial layer thicknesses also can result in three different movable
electrode thicknesses using the same masks, with each electromechanical
device accumulating a different number of solid layers above the
respective sacrificial layer. Thus, each movable electrode also can
acquire a different stiffness as a result of the different thicknesses.
Similarly, in implementations where the electromechanical devices are
IMODs, any etch stop layers kept in the device, either above or below the
air gap, can partially define the optical cavity.

[0078] FIGS. 9A-9H show examples of schematic cross-sections illustrating
an electromechanical device fabrication process including etch stops that
remain as part of the electromechanical device. In the illustrated
sequence, three different types of electromechanical systems structures
are formed, each having a different size air gap and different movable
electrode thicknesses. This implementation is suitable, for example, for
producing an IMOD display in which devices with different air gap sizes
represent different colors for sub-pixels of a color display.

[0079] Referring to FIG. 9A, a first sacrificial layer 905 is formed over
a stationary electrode 910 over a substrate 912. The first sacrificial
layer 905 can be formed by techniques known in the art, for example,
blanket deposition followed by masking, patterning, and etching (e.g.,
photolithographic patterning). In an IMOD implementation, the height of
the first sacrificial layer 905 can correspond to the size of the air gap
suitable for the electromechanical structure to display a desired color
when in the open state (see chart below). In the illustrated example, the
first sacrificial layer 905 has a height corresponding to
interferometrically enhanced reflection of the color blue in the
completed device. A person having ordinary skill in the art will readily
understand that the figures are simplified schematics and additional
layers, such as underlying or intervening buffer layers, black mask
layers, and bussing layers, may be present. For example, the stationary
electrode 910 can include multiple layers. The stationary electrode 910
can optionally include a transparent conductor. The dielectric layer or
layers over the conductors can serve as both an insulator to prevent the
electrodes from shorting during operation and an etch stop during
patterning of the first sacrificial layer.

[0080] Referring to FIG. 9B, a first stiffening layer 915 over the first
sacrificial layer 905 is deposited over the stationary electrode 910. For
the illustrated implementation, the first stiffening layer 915 includes a
material that is also suitable as an etch stop for patterning of a
sacrificial layer. For implementations where the electromechanical device
is an IMOD, the first stiffening layer 915 will ultimately become part of
the optical cavity. Accordingly, it can include a material that is
suitably transparent. For example, the first stiffening layer 915 can
include a material such as AlOx. Alternatively, the first stiffening
layer 915 can include any material that can act as an etch stop for the
first sacrificial layer 905. Specifically, a person having ordinary skill
in the art will readily recognize that the first stiffening layer 915 can
be any material that is resistant to the etchant and release chemistry
used to pattern the sacrificial layer 905, such as, e.g., silicon oxide
(SiO2), silicon nitride (Si3N4), silicon oxynitride
(SiON), etc. In some implementations, the first stiffening layer 915 can
be between about 30 Å and about 250 Å thick. For example, the
first stiffening layer 915 can be between about 80 Å and about 200
Å thick, or more particularly about 90-100 Å thick. The first
stiffening layer 915 can be deposited using, for example, a PVD
sputtering method, CVD, ALD, or other suitable deposition techniques.

[0081] Referring to FIG. 9C, subsequently, a second sacrificial layer 920
is formed over the first stiffening layer 915. The second sacrificial
layer 920 can be deposited and patterned using techniques and materials
similar to those of the first sacrificial layer 905. During the
patterning, and more particularly during etching of the sacrificial
material with the second mask (not shown) in place, the first stiffening
layer 915 serves as an etch stop to protect the first sacrificial layer
905 and the underlying stationary electrode 910. In the illustrated
example, the second sacrificial layer 920 has a height corresponding to
an interferometrically enhanced reflection of the color green in the
completed device.

[0082] Referring now to FIG. 9D, a second stiffening layer 925 is
deposited over the second sacrificial layer 920 and over the first
stiffening layer 915. The second stiffening layer 925 can be deposited
using techniques and materials similar to those of the first stiffening
layer 915. Next, in FIG. 9E, a third sacrificial layer 930 is formed over
the second stiffening layer 925. The third sacrificial layer 930 can be
deposited and patterned using techniques and materials similar to those
of the first and second sacrificial layers 905 and 920. During the
patterning, the second stiffening layer 925 serves as an etch stop to
protect the second sacrificial layer 920 from the etchant used for
patterning. In the illustrated example, the third sacrificial layer 930
has a height corresponding to an interferometrically enhanced reflection
of the color red in the completed device.

[0083] Subsequently, in FIG. 9F, a primary mechanical layer 935 is formed
over each of the three electromechanical structures. The primary
mechanical layer 935 can be formed by techniques known in the art, for
example, blanket deposition followed by masking, patterning, and etching.
In some implementations, the primary mechanical layer 935 can include
multiple layers such as, for example, a SiON layer sandwiched between
AlCu layers (see, e.g., FIG. 5D and attendant descriptions). In
implementations that include stiffening layers 915 and 925, such as the
illustrated implementation, the SiON layer can be substantially uniform.
Thus, in the illustrated implementation, a difference in stiffness
between different device types, corresponding to different gap sizes, is
created by the inclusion of a different number of stiffening layers 915
and 925 rather than a difference in the thickness of the primary
mechanical layer 935. This allows fewer processes to be used in the
creation of the primary mechanical layer 935, and no additional masks are
employed by blanket stiffening layers 915 and 925. In some
implementations, the SiON layer is between about 600 Å and about 1000
Å thick. For example, the SiON layer can be between about 700 Å
and about 900 Å thick, or more specifically about 800 Å thick. An
example to demonstrate the correspondence of stiffening layer thickness
to air gap size is shown in the below Table A. Table A also shows an
exemplary relationship between interferometric color and air gap size for
implementations where the electromechanical device is an IMOD.

[0084] Referring now to FIG. 9G, sidewall portions of the sacrificial
layers 905, 920, and 930 and the stiffening layers 915 and 925 are
removed from the areas between the three electromechanical structures.
The stiffening layers 915 and 925 can be removed using, e.g., sputter
etching or reactive ion etching (ME). Horizontal portions of the
stiffening layers are protected under the primary mechanical layer, and
portions between devices and the sidewalls of the sacrificial layers 905,
920, and 930 are removed, exposing the sacrificial layer sidewalls for
the subsequent "release etch" that opens the air gaps. Not shown are the
support structures (e.g., posts) that will hold up the moving electrodes.

[0085] Subsequently, in FIG. 9H, the sacrificial layers 905, 920 and 930
are selectively removed using the aforementioned release etch. Within the
electromechanical structures, the stiffening layers 915 and 925 remain in
place, becoming part of a movable electrode (such as the movable
electrodes 850a, 850b and 850c described above with respect to FIG. 8),
the stationary electrode 910, or both. Where the stiffening layers 915
and 925 remain in place, the stiffening layers may be considered part of
the stationary electrode 910. In an IMOD implementation, the stiffening
layers 915, 925 can be considered part of the optical stack, may be
referred to as optical layers, and partially define the optical path
length in both open (relaxed) and closed (actuated) states. In
electromechanical structures where one or more stiffening layers 915 and
925 combine with the primary mechanical layer 935, the combination
becomes stiffer and more resistant to deformation. Therefore, for the
same magnitude of actuation voltage applied across the electrodes 910 and
935, a stiffer mechanical layer will deflect a smaller distance. This
effect may allow an electromechanical driver to use similar voltages to
collapse or relax (e.g., with bias) different electromechanical types
having different air gap sizes.

[0086] Furthermore, while a different number of stiffening layers 915 and
925 are incorporated into the movable electrodes 935 of the three
different electromechanical types, the total number of stiffening layers
915 and 925 between the stationary electrode 910 and the movable
electrode 935 remains constant among the three different
electromechanical types. Therefore, the optical and physical distance
between the stationary electrode 910 and the movable electrode 935 will
be approximately constant among different electromechanical types when
they are in the collapsed state. In implementations where the
electromechanical devices are IMODs, having a constant optical distance
between the stationary electrode 910 and the movable electrode 935 in the
collapsed state simplifies design of the optical stack because the same
materials can be used for each of the three different electromechanical
types and the same appearance (e.g., black or white) will be generated in
the collapsed or actuated state. Note that the dielectric stack in the
collapsed state will generally include a common dielectric across the
stationary electrode 910 that is not separately illustrated.

[0087] A person having ordinary skill in the art will readily understand
that additional or fewer stiffening layers can be used to adjust the gap
between the stationary electrode 910 and the movable electrode 935 when
in the collapsed or actuated state. Similarly, the relative and absolute
thicknesses of the stiffening layers 915 and 925 can be adjusted in order
to modify the relative and absolute stiffnesses of the resulting movable
electrode stacks. For example, in order to increase the overall actuation
voltage, the absolute thickness can be increased by introducing
additional stiffening layers to the stiffening layers 915 and 925.
Alternatively, individual ones of the stiffening layers 915 and 925 can
be made thicker. On the other hand, in order to adjust the relative
actuation voltage between different electromechanical device types (for
example, to normalize actuation voltage), the stiffening layers 915 and
925 can be made with different relative thicknesses. Because each
electromechanical device type has a movable electrode 935 supported by a
different combination of stiffening layers, an increase in the thickness
of one stiffening layer will only increase the actuation voltage of a
subset of electromechanical devices in the array.

[0088] A person having ordinary skill in the art will also readily
understand that, in implementations where the electromechanical devices
are IMODs, the size of an optical cavity does not necessarily equal the
thicknesses of the respective sacrificial layer plus the cumulative
thickness of the stiffening layers 915 and 925. Rather, after the
sacrificial layers 905,920, and 930 are etched away, also referred to as
released, such that the movable electrodes 935 are free to move, the
movable electrodes 935 tend to respond to competing forces. First, the
movable electrodes 935 may tend to move away from the stationary
electrode 910 upon release due to inherent stresses in the mechanical
layer, thereby increasing the size of the optical cavity. This behavior
is known as a "launch effect" or producing a "launch angle." The
operational bias voltage of the MEMS device in a relaxed state typically
counteracts the launch angle by moving the movable electrodes 935 towards
the stationary electrode 910, thereby decreasing the optical cavity size.
The net result is that the absolute size of the optical cavity (which
includes the air gap and any transparent layers between the reflective
surfaces of the two electrodes) is approximately 10-15% smaller than the
thickness of the sum of the sacrificial layers and any etch stop layers.

[0089] As seen in Table A above, the air gap of a first electromechanical
device is formed by the removal of the first sacrificial layer, which is
about 1800 Å thick. When the sacrificial layer is etched and the
overlying mechanical layer is freed by release etching the sacrificial
layer, the resulting gap size reduces by about 10-15% due to a
combination of the "launch angle" caused by stress in the mechanical
layer (tending to increase the cavity size) and the operational voltage
that draws the upper electrode closer to the lower electrode even in the
"relaxed" position (tending to decrease the cavity size). This results in
an electromechanical device having a second order blue color, with an air
gap range about 310 nm and 390 nm, in the open or relaxed state. The air
gaps for the second and third electromechanical devices are described in
a similar fashion according to the chart above.

[0090] A person having ordinary skill in the art will also readily
understand that the present disclosure applies to electromechanical
systems with any number of different device types. FIGS. 10A and 10B
illustrate one implementation of an electromechanical device array having
only two different electromechanical device types, each with a different
gap size. FIG. 10A illustrates the devices in the open state, while FIG.
10B illustrates the devices in the collapsed state. FIGS. 10A and 10B are
similar to FIGS. 8A and 8B, respectively, with the omission of one
electromechanical device type, and similar parts are referred to by like
reference numerals.

[0091]FIG. 10A shows an example of a schematic cross-section of two
different electromechanical device types with both shown in the open
state having different sized air gaps and stiffening layers of different
thickness. In the illustrated implementation, an electromechanical system
device includes a substrate 800 on which two different types of
electromechanical structures are formed. The different electromechanical
structures each include a stationary electrode 816 and a movable
electrode 850a or 850b. The movable electrode 850a can include a primary
mechanical layer 860 and a mechanical sub-layer 870a. Conversely, the
movable electrode 850b can include only a primary mechanical layer 860,
with no mechanical sub-layer.

[0092] FIG. 10B shows an example of a schematic cross-section of the
devices of FIG. 10A in the collapsed state. As shown in the illustrated
implementation, air gaps 840a and 840b are no longer present when the
electromechanical devices are in the collapsed or actuated state. While
both electromechanical device types are shown in the collapsed state, a
person having ordinary skill in the art will readily understand that the
air gaps 840a and 840b can be independently opened and collapsed in any
combination.

[0093] FIGS. 11A-11F show examples of schematic cross-sections
illustrating an electromechanical device fabrication process including
etch stops that remain as part of the electromechanical device, for two
different electromechanical device types. In the illustrated sequence,
two different types of electromechanical systems structures are formed,
each having a different size air gap and different movable electrode
thicknesses. FIGS. 11A-11F are similar to FIGS. 9A-9H, with the omission
of one electromechanical device type, and similar parts are referred to
by like reference numerals. Accordingly, the second stiffening layer 925
and the third sacrificial layer 930 are omitted.

[0094] Referring to FIG. 11A, a first sacrificial layer 905 is formed over
a stationary electrode 910 over a substrate 912. Referring to FIG. 11B, a
first stiffening layer 915 over the first sacrificial layer 905 is
deposited over the stationary electrode 910. Referring to FIG. 11c,
subsequently, a second sacrificial layer 920 is formed over the first
stiffening layer 915. Subsequently, in FIG. 11D, a primary mechanical
layer 935 is formed and patterned over each of the two sacrificial layers
905 and 920 to define two different types of unreleased electromechanical
structures.

[0095] Referring now to FIG. 11E, sidewall portions of the sacrificial
layers 905 and 920 and the stiffening layer 915 is removed from the areas
between the two electromechanical structures. Removal of the sidewalls
and stiffening layer 915 can be accomplished in substantially the same
manner as described above with respect to FIG. 9G. Subsequently, in FIG.
11F, the sacrificial layers 905 and 920 are selectively removed using the
release etch described above with respect to FIG. 9H.

[0096]FIG. 12 shows an example of a flow chart illustrating a process of
fabricating different electromechanical device types with different
sacrificial layer thicknesses. In the illustrated implementation, a
manufacturing process 1200 fabricates an electromechanical device
corresponding to the cross-sectional schematic illustrations of FIGS.
11A-11D. In some implementations, the manufacturing process 1200 can be
implemented to manufacture, e.g., interferometric modulators of the
general type illustrated in FIGS. 1 and 5A-5E, in addition to other
blocks not shown in FIG. 12. With reference to FIG. 12, the process 1200
begins at block 1210 with the provision of a substrate. The process 1200
continues at block 1220 with the formation of a stationary electrode
layer over the substrate. Next, the process 1200 continues at block 1230
with the formation of the first sacrificial layer over the stationary
electrode in a first region. Then, the process 1200 continues at block
1240 with the formation of a first stiffening layer over the first
sacrificial layer in the first region. Subsequently, the process 1200
continues at block 1250 with the formation of a second sacrificial layer
over the stationary electrode layer in the second region. The process
1200 continues at block 1260 with the formation of a movable electrode
layer over the first and second sacrificial layers, respectively.

[0097] FIGS. 13A and 13B show examples of system block diagrams
illustrating a display device 40 that includes a plurality of
interferometric modulators. The display device 40 can be, for example, a
cellular or mobile telephone. However, the same components of the display
device 40 or slight variations thereof are also illustrative of various
types of display devices such as televisions, e-readers and portable
media players.

[0098] The display device 40 includes a housing 41, a display 30, an
antenna 43, a speaker 45, an input device 48, and a microphone 46. The
housing 41 can be formed from any of a variety of manufacturing
processes, including injection molding, and vacuum forming. In addition,
the housing 41 may be made from any of a variety of materials, including,
but not limited to: plastic, metal, glass, rubber, and ceramic, or a
combination thereof. The housing 41 can include removable portions (not
shown) that may be interchanged with other removable portions of
different color, or containing different logos, pictures, or symbols.

[0099] The display 30 may be any of a variety of displays, including a
bi-stable or analog display, as described herein. The display 30 also can
be configured to include a flat-panel display, such as plasma, EL, OLED,
STN LCD, or TFT LCD, or a non-flat-panel display, such as a CRT or other
tube device. In addition, the display 30 can include an interferometric
modulator display, as described herein.

[0100] The components of the display device 40 are schematically
illustrated in FIG. 13B. The display device 40 includes a housing 41 and
can include additional components at least partially enclosed therein.
For example, the display device 40 includes a network interface 27 that
includes an antenna 43 which is coupled to a transceiver 47. The
transceiver 47 is connected to a processor 21, which is connected to
conditioning hardware 52. The conditioning hardware 52 may be configured
to condition a signal (e.g., filter a signal). The conditioning hardware
52 is connected to a speaker 45 and a microphone 46. The processor 21 is
also connected to an input device 48 and a driver controller 29. The
driver controller 29 is coupled to a frame buffer 28, and to an array
driver 22, which in turn is coupled to a display array 30. A power supply
50 can provide power to all components as required by the particular
display device 40 design.

[0101] The network interface 27 includes the antenna 43 and the
transceiver 47 so that the display device 40 can communicate with one or
more devices over a network. The network interface 27 also may have some
processing capabilities to relieve, e.g., data processing requirements of
the processor 21. The antenna 43 can transmit and receive signals. In
some implementations, the antenna 43 transmits and receives RF signals
according to the IEEE 16.11 standard, including IEEE 16.11(a), (b), or
(g), or the IEEE 802.11 standard, including IEEE 802.11a, b, g or n. In
some other implementations, the antenna 43 transmits and receives RF
signals according to the BLUETOOTH standard. In the case of a cellular
telephone, the antenna 43 is designed to receive code division multiple
access (CDMA), frequency division multiple access (FDMA), time division
multiple access (TDMA), Global System for Mobile communications (GSM),
GSM/General Packet Radio Service (GPRS), Enhanced Data GSM Environment
(EDGE), Terrestrial Trunked Radio (TETRA), Wideband-CDMA (W-CDMA),
Evolution Data Optimized (EV-DO), 1xEV-DO, EV-DO Rev A, EV-DO Rev B, High
Speed Packet Access (HSPA), High Speed Downlink Packet Access (HSDPA),
High Speed Uplink Packet Access (HSUPA), Evolved High Speed Packet Access
(HSPA+), Long Term Evolution (LTE), AMPS, or other known signals that are
used to communicate within a wireless network, such as a system utilizing
3G or 4G technology. The transceiver 47 can pre-process the signals
received from the antenna 43 so that they may be received by and further
manipulated by the processor 21. The transceiver 47 also can process
signals received from the processor 21 so that they may be transmitted
from the display device 40 via the antenna 43.

[0102] In some implementations, the transceiver 47 can be replaced by a
receiver. In addition, the network interface 27 can be replaced by an
image source, which can store or generate image data to be sent to the
processor 21. The processor 21 can control the overall operation of the
display device 40. The processor 21 receives data, such as compressed
image data from the network interface 27 or an image source, and
processes the data into raw image data or into a format that is readily
processed into raw image data. The processor 21 can send the processed
data to the driver controller 29 or to the frame buffer 28 for storage.
Raw data typically refers to the information that identifies the image
characteristics at each location within an image. For example, such image
characteristics can include color, saturation, and gray-scale level.

[0103] The processor 21 can include a microcontroller, CPU, or logic unit
to control operation of the display device 40. The conditioning hardware
52 may include amplifiers and filters for transmitting signals to the
speaker 45, and for receiving signals from the microphone 46. The
conditioning hardware 52 may be discrete components within the display
device 40, or may be incorporated within the processor 21 or other
components.

[0104] The driver controller 29 can take the raw image data generated by
the processor 21 either directly from the processor 21 or from the frame
buffer 28 and can re-format the raw image data appropriately for high
speed transmission to the array driver 22. In some implementations, the
driver controller 29 can re-format the raw image data into a data flow
having a raster-like format, such that it has a time order suitable for
scanning across the display array 30. Then the driver controller 29 sends
the formatted information to the array driver 22. Although a driver
controller 29, such as an LCD controller, is often associated with the
system processor 21 as a stand-alone Integrated Circuit (IC), such
controllers may be implemented in many ways. For example, controllers may
be embedded in the processor 21 as hardware, embedded in the processor 21
as software, or fully integrated in hardware with the array driver 22.

[0105] The array driver 22 can receive the formatted information from the
driver controller 29 and can re-format the video data into a parallel set
of waveforms that are applied many times per second to the hundreds, and
sometimes thousands (or more), of leads coming from the display's x-y
matrix of pixels.

[0106] In some implementations, the driver controller 29, the array driver
22, and the display array 30 are appropriate for any of the types of
displays described herein. For example, the driver controller 29 can be a
conventional display controller or a bi-stable display controller (e.g.,
an IMOD controller). Additionally, the array driver 22 can be a
conventional driver or a bi-stable display driver (e.g., an IMOD display
driver). Moreover, the display array 30 can be a conventional display
array or a bi-stable display array (e.g., a display including an array of
IMODs). In some implementations, the driver controller 29 can be
integrated with the array driver 22. Such an implementation is common in
highly integrated systems such as cellular phones, watches and other
small-area displays.

[0107] In some implementations, the input device 48 can be configured to
allow, e.g., a user to control the operation of the display device 40.
The input device 48 can include a keypad, such as a QWERTY keyboard or a
telephone keypad, a button, a switch, a rocker, a touch-sensitive screen,
or a pressure- or heat-sensitive membrane. The microphone 46 can be
configured as an input device for the display device 40. In some
implementations, voice commands through the microphone 46 can be used for
controlling operations of the display device 40.

[0108] The power supply 50 can include a variety of energy storage devices
as are well known in the art. For example, the power supply 50 can be a
rechargeable battery, such as a nickel-cadmium battery or a lithium-ion
battery. The power supply 50 also can be a renewable energy source, a
capacitor, or a solar cell, including a plastic solar cell or solar-cell
paint. The power supply 50 also can be configured to receive power from a
wall outlet.

[0109] In some implementations, control programmability resides in the
driver controller 29 which can be located in several places in the
electronic display system. In some other implementations, control
programmability resides in the array driver 22. The above-described
optimization may be implemented in any number of hardware and/or software
components and in various configurations.

[0110] The various illustrative logics, logical blocks, modules, circuits
and algorithms described in connection with the implementations disclosed
herein may be implemented as electronic hardware, computer software, or
combinations of both. The interchangeability of hardware and software has
been described generally, in terms of functionality, and illustrated in
the various illustrative components, blocks, modules, circuits and
processes described above. Whether such functionality is implemented in
hardware or software depends upon the particular application and design
constraints imposed on the overall system.

[0111] The hardware and data processing apparatus used to implement the
various illustrative logics, logical blocks, modules and circuits
described in connection with the aspects disclosed herein may be
implemented or performed with a general purpose single- or multi-chip
processor, a digital signal processor (DSP), an application specific
integrated circuit (ASIC), a field programmable gate array (FPGA) or
other programmable logic device, discrete gate or transistor logic,
discrete hardware components, or any combination thereof designed to
perform the functions described herein. A general purpose processor may
be a microprocessor, or, any conventional processor, controller,
microcontroller, or state machine. A processor may also be implemented as
a combination of computing devices, e.g., a combination of a DSP and a
microprocessor, a plurality of microprocessors, one or more
microprocessors in conjunction with a DSP core, or any other such
configuration. In some implementations, particular processes and methods
may be performed by circuitry that is specific to a given function.

[0112] In one or more aspects, the functions described may be implemented
in hardware, digital electronic circuitry, computer software, firmware,
including the structures disclosed in this specification and their
structural equivalents thereof, or in any combination thereof.
Implementations of the subject matter described in this specification
also can be implemented as one or more computer programs, i.e., one or
more modules of computer program instructions, encoded on a computer
storage media for execution by, or to control the operation of, data
processing apparatus.

[0113] Various modifications to the implementations described in this
disclosure may be readily apparent to those skilled in the art, and the
generic principles defined herein may be applied to other implementations
without departing from the spirit or scope of this disclosure. Thus, the
disclosure is not intended to be limited to the implementations shown
herein, but is to be accorded the widest scope consistent with the
claims, the principles and the novel features disclosed herein. The word
"exemplary" is used exclusively herein to mean "serving as an example,
instance, or illustration." Any implementation described herein as
"exemplary" is not necessarily to be construed as preferred or
advantageous over other implementations. Additionally, a person having
ordinary skill in the art will readily appreciate, the terms "upper" and
"lower" are sometimes used for ease of describing the figures, and
indicate relative positions corresponding to the orientation of the
figure on a properly oriented page, and may not reflect the proper
orientation of the IMOD as implemented.

[0114] Certain features that are described in this specification in the
context of separate implementations also can be implemented in
combination in a single implementation. Conversely, various features that
are described in the context of a single implementation also can be
implemented in multiple implementations separately or in any suitable
subcombination. Moreover, although features may be described above as
acting in certain combinations and even initially claimed as such, one or
more features from a claimed combination can in some cases be excised
from the combination, and the claimed combination may be directed to a
subcombination or variation of a subcombination.

[0115] Similarly, while operations are depicted in the drawings in a
particular order, this should not be understood as requiring that such
operations be performed in the particular order shown or in sequential
order, or that all illustrated operations be performed, to achieve
desirable results. In certain circumstances, multitasking and parallel
processing may be advantageous. Moreover, the separation of various
system components in the implementations described above should not be
understood as requiring such separation in all implementations, and it
should be understood that the described program components and systems
can generally be integrated together in a single software product or
packaged into multiple software products. Additionally, other
implementations are within the scope of the following claims. In some
cases, the actions recited in the claims can be performed in a different
order and still achieve desirable results.